In high speed and high ramp machinings, a radially outward force is applied to a cutting insert, which is mounted in a milling cutter, due to a centrifugal force and a radially outward cutting force. Such a radially outward force acts to push the cutting insert from an insert pocket of the milling cutter radially outwardly of the insert pocket, thus restricting a cutting edge feed and a depth of cut. Further, said radially outward force minutely displaces the cutting insert in a radially outward direction, thereby leading to the breakage of a clamping screw for securing the cutting insert to the insert pocket and the separation of the cutting insert from the milling cutter. As such, the failure of firmly retaining the cutting insert in the insert pocket of the milling cutter during the high speed machining and high ramp machining may lead to the breakage of the clamping screw, the separation of the cutting insert, and the damages of the milling cutter and workpieces. In particular, if the cutting insert is not firmly retained when machining the workpieces such as aircraft parts at a high speed, then the workpieces cannot be precisely machined.
As to the retention between the cutting insert and the insert pocket, U.S. Pat. No. 5,542,795 proposes a milling cutter wherein a rail of a cutting insert is fitted to a slot of an insert pocket. According to this document, the cutting insert is mounted to the milling cutter such that the rail protruding from a bottom surface of the cutting insert is fitted to the slot formed in a base wall of the insert pocket. If the cutting insert is mounted in the insert pocket, then a peripheral surface of the cutting insert, which does not face toward a workpiece, contacts a side wall of the insert pocket and the bottom surface of the cutting insert contacts the base wall of the insert pocket. Further, a flat bottom surface of the rail contacts a flat bottom surface of the slot.
In the aforementioned prior art milling cutter, to mount the cutting insert in the insert pocket, the bottom surface of the rail and the peripheral surface and the bottom surface of the cutting insert must come into contact with the bottom surface of the slot and the side wall and the base wall of the insert pocket, respectively. To accomplish such contact, the cutting insert and the insert pocket require strict tolerance maintenance and high precision. This does not facilitate the manufacture of a cutting insert and a milling cutter, which are stably usable in a high speed machining as well as a high ramp machining.